Various intrinsically-conductive polymers already exist that possess non-linear properties when exposed to an electric field. Numerous prior art patents disclose such compounds, for example French patent No. 96/10963 in the name of the Applicant.
Copolymers possessing ferromagnetic properties have been developed by the Applicant in European patent EP-A-0 545 819. Those copolymers comprise amino-aromatic groups based on a structural unit comprising a first group of amino-aromatic compounds chosen from aniline derivatives and the corresponding iminoquinone forms; and a second group of substituted amino-aromatic compounds chosen from substituted amino compounds containing at least two condensed benzene rings, substituted polycyclic compounds containing at least one aniline structural unit in their structure, compounds derived from aniline and carrying a substituent bonded to the ring by means of an ethynylidene or paraphenylene link, and the corresponding immunoquinone compounds. Nevertheless, those compounds do not possess sufficient magnetic and electrical properties simultaneously.
The person skilled in the art already knows means for synthesizing polyaniline in order to obtain improved non-linear ferromagnetic properties and electrical properties. For example, it is known to dissolve the polyaniline in its neutral form in N methyl pyrrolidone (NMP) and to react the solution with an aqueous iron sulfate solution, and then to re-dope it by the action of hydrochloric acid. That method thus comprises a plurality of distinct steps. The method of the invention makes it possible in a single step to synthesize a polyaniline having both magnetic properties and improved non-linear electrical properties.
The resulting compound can be used in cables for use in the telecommunications field. Such cables are coaxial in structure and are made up of a metal core surrounded by at least two layers, one of which is a layer of dielectric material including the material of the invention and intrinsically filtering the electromagnetic disturbances they convey. The use of the material of the invention makes it possible to provide better matching for the cutoff frequency of filtering cables. This is particularly advantageous for filtering cables of short length.